Minerals geology

Ions are charged atoms • Cations are positively charged whereas • Anions are negatively charged Common ions in earth's crust: O - most common ion anion Si, Al, Fe, Ca, Na, K, Mg, Ca

Dr R B Schultz

The earth is made of rocks, which are in turn made of minerals In this part of the course we'll learn how

to identify common minerals and rocks.

must meet five (5) criterion:

Minerals are:

·        1 Naturally occurring,

·        2 Inorganic,

·        3 Have known chemical compositions

·        4 Have definite physical properties.

5 Are solid

·       

They are usually (although not always)

crystalline.

Minerals are classified based on chemical composition and crystal structure

Minerals are made of different ions bonded together

Ions are charged atoms

•         Cations are positively charged whereas

•         Anions are negatively charged

Common ions in earth's crust:

O - most common ion (anion)

Si, Al, Fe, Ca, Na, K, Mg, (Cations)

Minerals are made mainly of these ions

Crystal structure

Crystal structure depends on sizes of and charges on ions

Polymorphs same chemical composition, different crystal structures

Mafic silicate minerals

Most common minerals are silicates

All silicate minerals contain silicon and oxygen

Silicates that also contains iron or magnesium are called mafic silicate minerals

Mafic silicate minerals are dark in color

Examples: of mafic silicates: olivine, pyroxene, amphibole, and biotite mica

Felsic silicates

Felsic silicates are silicate minerals that don't contain magnesium or iron, are light in color

Examples: feldspar, quartz, clay minerals, muscovite mica

Silicate mineral structures

Basic building block: silica tetrahedron

Silica tetrahedron is a silicon ion bonded to 4 oxygen ions

Silicon is positively charged (+4)

Oxygen is negatively charged (-2)

Net charge on tetrahedron: -4

Because tetrahedron is negatively charged, it is attracted to cations

Tetrahedra may link together by a cation (e.g Mg, Fe, Na, Ca, K) serving as a bridge, or

Tetrahedra may link together by sharing oxygens

Isolated tetrahedral structure

Cations serve as links between tetrahedra; no sharing of oxygens

e.g olivine, and garnet, which also happen to be mafic silicates

Single chain silicates

Adjacent tetrahedra form a chain by sharing 2 of their oxygens with neighboring tetrahedra

e.g pyroxenes, which also happen to be mafic silicates

Double chain silicates

Two chains can link up by sharing oxygens

e.g amphiboles, which are mafic silicates too

Sheet silicates

Sheets are formed when each tetrahedron shares 3 of its oxygens with its neighbors

e.g micas, biotite (mafic) and muscovite (non-mafic), and clay minerals, which are non-mafic silicates

Framework silicates

Every oxygen in each tetrahedron is shared to form 3-D framework

e.g feldspar, quartz, which are also non-mafic

Common non-silicate minerals

Calcite calcium carbonate Limestone is made of calcite

Dolomite calcium magnesium carbonate

Gypsum calcium sulfate

Galena lead sulfide

Pyrite iron sulfide

Halite sodium chloride (table salt)

How to Identify Minerals: Physical Properties

Geologists determine the identity of an unknown mineral by describing its physical properties They then use a reference book to find out what mineral has those properties We will learn to describe the physical properties

1 Habit refers to the overall shape of the mineral

use terms like: "equant" (3 dimensions of the mineral have about the same length, like a cube or sphere),

“elongate" (one direction is long but the other 2 are short, like a pencil), or "platy" (one dimension is short, other 2 are long like a sheet of paper)

isolated tetrahedra & framework silicate minerals tend to be equant in habit; chain silicates tend to be elongate, sheet silicates are platy

2 Cleavage

Refers to very smooth, flat, shiny breakage surfaces

These special breakage surfaces correspond to zones of weak bonding in the crystal structure

To describe cleavage, must determine the number of unique cleavage planes (directions) and their angle with respect to each other (e.g salt breaks into cubes, with cleavage in 3 directions, all at 90 degrees)

3 Hardness

Refers to "scratchability" of the minerals harder minerals will scratch softer minerals

Rank minerals according to hardness using the Moh's scale

Fingernails are about 2.5 on Moh's scale; glass or steel knife is about 5.5; use these common items to estimate hardness of a mineral

4 Color

Varies in many minerals, e.g quartz

Some minerals come in just one color; other are many colors/many varieties

Some minerals are magnetic

Some minerals effervesce ("fizz") in dilute acid

Specific gravity (like density)

Moh's Hardness Scale (Commit this to memory)

  1.0      TALC

Crystal structure

Crystal structure depends on sizes of and charges on ions  

All silicate minerals contain silicon and oxygen

1 Mafic silicate minerals contain iron or magnesium and

are dark in color

Examples: olivine, pyroxene, amphibole, and biotite

mica

2 Felsic silicates don't contain magnesium or iron, and

are light in color

Examples: feldspar, quartz, clay minerals, muscovite

mica

Mafic silicate Felsic silicate

Silicate mineral structures

Basic building block: silica tetrahedron

Silica tetrahedron is a silicon ion bonded to 4 oxygen ions

Silicon is positively charged (+4)

Oxygen is negatively charged (-2)

Net charge on tetrahedron: -4

Because entire tetrahedron is negatively charged, it is

attracted to cations

Tetrahedra may link together by a cation (e.g Mg, Fe, Na,

Ca, K) serving as a bridge, or may link together by sharing oxygens

Silica

Tetrahedron

Isolated tetrahedral structure

Cations serve as links between tetrahedra; no sharing of oxygens

e.g olivine, and garnet, which also happen to be mafic silicates

Single chain silicates

Adjacent tetrahedra form a chain by sharing 2 of their oxygens with

neighboring tetrahedra

e.g pyroxenes, which also happen to be mafic silicates

Double chain silicates

Two chains can link up by sharing oxygens

e.g amphiboles, which are mafic silicates too

Every oxygen in each tetrahedron is shared to form 3-D framework

e.g feldspar, quartz, which are also non-mafic

Common non-silicate minerals

Fluorite – used as a toothpaste additive

Calcite calcium carbonate Limestone is made of calcite Dolomite calcium magnesium carbonate

Gypsum calcium sulfate

Galena lead sulfide

Pyrite iron sulfide

Halite sodium chloride (table salt)

How to Identify Minerals: Physical Properties

Geologists determine the identity of an unknown mineral by describing its

physical properties They then use a reference book to find out what mineral has those properties We will learn to describe the physical

properties

1 Habit refers to the overall shape of the mineral Scientists use terms like: "equant" (3 dimensions of the mineral have about the same length, like a cube or sphere), “elongate" (one direction is long but the other 2 are short, like a pencil), or "platy" (one dimension is short, other 2 are long like a sheet of paper)

One of the first determinations a geologist must make is whether the mineral in metallic or non-metallic.

Non-metallic mineral

Metallic mineral

Refers to very smooth, flat, shiny breakage surfaces

These special breakage surfaces correspond to zones of weak bonding in the crystal structure

To describe cleavage, one must determine the number of unique cleavage planes (directions) and their angle with respect to each other (e.g salt breaks into cubes,

with cleavage in 3 directions, all at 90 degrees)

NO cleavage

Varies in many minerals, e.g quartz

VERY unreliable.

Some minerals come in just one color;

other are many colors/many varieties.

Streak

Refers to color of mark left by rubbing mineral against a streak plate (unglazed porcelain) Streak does not vary even if color does

Other Properties

Some minerals are magnetic (i.e., magnetite)

Some minerals effervesce ("fizz") in dilute acid (calcite)

Specific gravity (like density) galena has a high specific gravity

Mineral Chemical composition

Key Terminology

Pertinent Web Sites Amateur Mineralogy Links

A very extensive listing of links to sites related to mineralogy.

Ask a Geologist

If you have questions, a professional geologist is here to help.

Ecole des Mines de Paris Mineralogy

Here are some beautiful mineral pictures from a museum in Paris.

Gems and Precious Stones

Jill Banfield's (University of Wisconsin-Madison) integrated body of information about gems and gemstones.

Gold Institute

A good commercial site with a lot of information about gold.

Gold Prospecting

A good source for information about recreational gold prospecting.

Mineral and Gemstone Kingdom

This site contains a comprehensive list of minerals and their properties.

Mineral and Rock Description (National Park Service)

Mineral and rock photographs and descriptions from the National Park Service.

Mineral Data Links

Links to several mineralogy related Web sites.

Mineral Descriptions and Images

The Mineral Gallery is a constantly growing collection of mineral descriptions, images, and specimens, together with several ways of accessing these descriptions.

Mineralogy and Petrology Research on the Web

An extensive list of mineralogy and petrology resources on the Web.

Mineralogy Database

This extensive mineral database contains more than 5,000 pages of mineral data There are 3,874 individual mineral species data descriptions.

Mineralogy Links (University of Oxford)

An extensive listing of mineralogy and minerals related sites.

Mineral Identification Tutorial

Mineral identification tutorial from Texas A & M University.

Mineral Photographs

A comprehensive collection of mineral and gemstone photographs from The Image.

Mineral Resources Program (USGS)

The USGS Mineral Resources Program is responsible for providing and communicating current, unbiased information on the occurrence, quality, quantity, and availability of mineral resources.

Minerals Links (Houghton Mifflin)

Links to several mineral sites, including class lecture notes, arranged by topic.

Minerals Links (NAGT)

An extensive listing of mineral links arranged by topic from the National Association of Geology Teachers (NAGT).

Minerals Links (University of Würzburg)

An extensive listing of mineral links including mineral descriptions and thin section images.

Minerals (Mineralogical Society of America)

The Mineralogical Society of America web site offers a good, general description of mineral properties, classification, etc directed primarily toward K-12 grade students.

Minerals (Trinity Mineral Company)

Beautiful photos of rare minerals offered for sale by the Trinity Mineral Company.

Minerals Information (USGS)

United States Geologic Survey (USGS) statistics and information on the worldwide supply, demand, and flow of minerals and materials essential

to the U.S economy, the national security, and protection of the environment.

Minerals on the Internet

A wide variety of minerals-related sites sorted into relevant categories from Tasa Graphic Arts, Inc.

Mining and Mineral Resources

A great source for information about mining of mineral resources, mining news and trends, etc.

National Mining Association

The National Mining Association (NMA) represents the mining industry, mining equipment manufacturers, and other mining-related businesses, throughout the United States.

Periodic Table of the Elements

Periodic Table of the Elements II

A great source for information on the elements.

Resource Fact Sheets (USGS)

United States Geological survey (USGS) activities in the natural resources theme area inventory the occurrence and assess the quantity and quality of natural resources Activities also include monitoring changes to natural resources, understanding the processes that form and affect them, and forecasting the changes that may be expected in the future.

Resources from Space

University of Wisconsin course notes with links to several essays about resources from space.

Resource Sustainability

An essay that examines the future of Earth's resources.

Rock and Mineral Collecting (USGS)

Selected references on rocks, minerals, and gemstones from the United States Geological Survey (USGS).

Rockhounds Information Page

The Rockhounds Information Page offers many links to mineral and rock related Websites.

Smithsonian Gem & Mineral Collection

Images of mineral and gemstone specimens found in the Smithsonian Institution (Not an official Smithsonian site)

Society for Mining, Metallurgy and Exploration, Inc

The Society for Mining, Metallurgy, and Exploration (SME) is an international society of professionals in the minerals industry.

Society of Economic Geologists

The Society of Economic Geologists, Inc (SEG) is an international organization of individual members with interests in the field of economic geology.

State Minerals Information (USGS)

Statistics and information on the supply, demand, and flow of minerals and materials essential to the U.S economy, the national security, and protection of the environment from the United States Geological Survey (USGS).

Technical University of Clausthal

This site at a German university also shows some excellent mineral pictures.

Virtual Atlas of Opaque and Ore Minerals

This site provides over 400 full colour photomicrographs of the major ore-forming associations and opaque minerals in non-mineralized rocks It describes typical examples of each material from many classical localities throughout the world For each association there is a listing of the major (and important minor) primary ore minerals, alteration products and gangue, typical textures, a brief discussion of the geology of the association and a list of references

World Lecture Hall (University of Texas at Austin)

The World Lecture Hall features links to online courses in the United States and Canada.

Simplest to use for Mineral I.D Lab:

Virtual Rock Bag

http://comp.uark.edu/~sboss/vrockbag.htm#minerals